Relationship of Dopamine to Cognitive Function in Parkinson's Disease

This study will examine how the brain chemical dopamine affects memory, reasoning, and other thought processes in people with Parkinson's disease with and without dementia and in healthy control subjects. Healthy normal volunteers and people with Parkinson's disease who are between 40 and 85 years of age may be eligible for this study. Pregnant women with Parkinson's disease and breastfeeding normal volunteers are excluded. Candidates are screened with a physical and neurological examination, blood tests, a brief mental test called the Mini Mental Status Examination, and other tests designed to assess memory, learning, reasoning, and other thought processes. Patients with Parkinson's disease also undergo a more thorough mental evaluation called the Mattis Dementia Rating Scale. The study requires about 15 hours over 4 or 5 outpatient visits to NIH. Participants undergo two positron emission tomography (PET) scans on two separate days and a magnetic resonance imaging (MRI) scan, as follows: PET Scans The two PET procedures are done the same way, except one uses a radioactive tracer called \[(18)F\]DOPA and one uses a tracer called \[(11)C\]NNC-112. A catheter (small plastic tube) is placed in a vein in the subject's arm for injection of the tracer. The subject lies on the scanner bed and a special mask is fitted to his or her head to hold it in place during the procedure. Just before injecting the tracer, a 10-minute "transmission scan" is done of the head using a tracer called (68)Ge. Then, a series of scans using one of the two study tracers (\[(18)F\]DOPA or \[(11)C\]NNC-112 are done for about 90 minutes. About 1 hour before injection of the \[(18)F\]DOPA tracer, subjects take 200 mg of the drug carbidopa by mouth to help the tracer work properly. Blood pressure, breathing and heart are monitored before and after injection of the \[(11)C\]NNC-112 tracer. Patients with Parkinson's disease are taken off all Parkinson's medications the night before the \[(18)F\]DOPA scan and their motor function is tested the following morning before the scans are done, using the Unified Parkinson's Disease Rating Scale. Patients can resume all medications except L-DOPA (including Sinemet) after the movement test, and they can resume L-DOPA after the PET scan is finished. MRI Scan MRI uses a strong magnetic field and radio waves to obtain images of the brain. The subject lies still on a table that slides inside the scanner, a metal cylinder. They wear ear plugs to muffle loud knocking sounds that occur during the scanning and can communicate with the MRI staff at any time through an intercom.